Effects of Sublethal Phoxim Exposure and Lower Food Intake on Nutrient Metabolism in the Midguts of Bombyx Mori

Silkworm (Bombyx mori) is an economically important insect. However, the survival of silkworms has been significantly affected by the assault of chemical pesticides on mulberry trees through aerial application and water currents. Phoxim is a broad-spectrum organophosphorus insecticide widely used in China. Currently, very little is known about the non-neuronal effects of sublethal exposure to phoxim. The purpose of this study was to investigate the non-neuronal effects of sublethal phoxim exposure in the silkworm midgut, with a focus on nutrient metabolism. After phoxim treatment, lipase activity in the silkworm was shown to be up-regulated at 24 h before a decreasing trend was seen. Meanwhile, α-amylase activity showed the opposite trend. The expression levels of mitochondrial respiratory chain-related genes were all up-regulated at 24 h before falling continuously. To ensure that the effects of phoxim on nutrient metabolism were not simply a consequence of a decrease in mulberry consumption, the silkworms were treated with a reduced-food diet before the digestive enzyme activities and the transcription levels of mitochondrial respiratory chain-related genes were analyzed. Our results showed that the patterns in the reduced-diet and phoxim-exposed silkworm were markedly different, suggesting the alterations in the phoxim-exposed silkworm cannot readily be explained by nutrient deprivation.